The present invention relates to light processors and more specifically to digital light processors that eliminate the need for micro-mirror devices.
Space light modulators are transducers that modulate incident light in a spatial pattern corresponding to an electrical or optical input. The incident light may be modulated in its phase, intensity, polarization, or direction, and the light modulation may be achieved by using elements made of a variety of materials exhibiting various electro-optic or magneto-optic effects and by materials that modulate light by surface deformation.
Digital light processors (DLP) are light modulators suitable for various applications such as displays, projectors, televisions, monitors and printing. DLP devices use movable micro-mirrors to direct light into a projector lens, which focuses and magnifies the modulated light from each micro-mirror onto a display screen to produce an image. Since each micro-mirror represents a pixel of light or an image, a DLP device typically consists of a high density array of micro-mirrors on a single-chip integrated circuit. Each micro-mirror rotates about a fixed axis to cause light to be controllably deflected by the rotation. Thus, in some applications, an array of such micro-mirrors can be positioned so that the individual mirrors making up pixels are selectively rotated to create patterns for various purposes.
FIG. 1 shows two DLP cells with mirrors 100 and 102 on the top surface of each cell. Each mirror is attached to an underlying yoke that rotates on a torsion hinge, until the landing tips of the yoke contact the underlying landing pad sites. The micro-mirrors are tilted to reflect light onto and away from the projection screen, as desired. The tilting of the hinged mirrors as shown may be achieved by electro-static actuation.
However, one problem with conventional DLP devices is the problem of stuck mirrors, where the landing tips are slow to lift from the pads or become permanently stuck to the pads. This ‘sticking problem’ is an important consideration for reliable performance, since it is the most frequent cause of device failure. Sources of the sticking problem may include moisture in the package, scrubbing of landing tips onto the metal landing pads, and outgassing of the epoxy sealants used in the manufacturing process for mounting the devices in their packages.
Solutions to the sticking problem have included applying lubrication or a passivation layer to the metal surfaces, using resonant reset methods to pump energy into the pixel element to help free it from the surface, and adding gettering material to absorb moisture within the package. More recently, ‘spring-tips’ have been added to the tips of the mirrors. U.S. Pat. No. 6,583,921 addresses the problem by using a non-contacting hinge geometry that eliminates physical contact between the mirrors and the landing pads.
However, the above solutions fail to address other problems. For example, the hinge itself may become damaged or defective. Moreover, some of the above solutions suffer from long-term degradation of the passivant, which could drive the technology to require hermetic packages and complex process steps. Other problems that remain unaddressed include heating of the chip and difficult thermal management of the micro-mirrors, which must be cooled. An additional problem is the “pixel effect” or background noise characterized by stray points of light appearing on the display screen. The pixel effect may typically be reduced by blurring the image so that the pixels surrounding the noise pixels are blended.
Thus, it is desirable to provide systems and methods that overcome the above and other problems. In particular, there is a need for a DLP device that eliminates problems such as stuck mirrors and the pixel effect, while minimizing processing complexity and fabrication steps.